ABS (antilock system) prevents the wheels from locking and comes into operation when greater adhesion than is transferable is demanded between a tire and the road, that is to say when the driver overbrakes. In overbraking, the central electronic control apparatus of the ABS brake system detects from rotational speed sensor signals the tendency of one or more wheels to lock and from this calculates the activation of the pressure control valve arrangement acting upon the assigned brake cylinder. The brake pressure is then set to optimal slip by the pressure control valve arrangement by lowering, holding or building up the brake pressure according to the wheel behavior and therefore the frictional conditions between the tire and road. ABS pressure control valve arrangements without a relay action, to which the exemplary embodiments and/or exemplary methods of the present invention relate, are used in vehicles, such as, for example, utility vehicles, omnibuses, tractors and trailers. Pressure control valve arrangements without a relay action mostly have 3/2 way solenoid valves as the pilot control valves of diaphragm valves, an electronic control device activating the 3/2 way solenoid valves so that the “pressure holding”, “pressure reduction” and the “pressure build-up” functions necessary for ABS operation can be carried out. During braking without the response of the ABS (no tendency of a wheel to lock), the pressure medium, mostly air, flows, unimpeded, through the pressure control valve arrangements in both directions when the brake cylinders are being ventilated and bled. This ensures that the functioning of the service brake system is not influenced by the ABS pressure control valve arrangement.
Pressure control valves of the generic type, as 1-channel pressure control valves for antilock systems in motor vehicles, have in each case, inside the housing, a diaphragm valve as a holding valve and as an outlet valve and also in each case an electromagnetic control valve for the holding valve and the outlet valve. The two diaphragm valves contain in each case a diaphragm capable of being acted upon by the pressure in a pilot control space, the pilot control space being closed outwardly by a cover fastened to the housing. A generic pressure control valve arrangement of an ABS brake system is known, for example, from EP 0 266 555 A1 or from DE-A 2 855 876. In the pressure control valve arrangements of the prior art, the housing has a pressure medium connection for the action of pressure and/or the relief of pressure, which is connected to a foot-operated brake valve. Furthermore, the two diaphragm valves are arranged laterally on the housing, the corresponding pilot control spaces being closed by covers fastened laterally to the housing, that is to say, there, surface normals on the diaphragms of both diaphragm valves are arranged perpendicularly to the mid-axis of the pressure medium connection.
Furthermore, in the published references, particularly according to FIG. 1 of DE-A-2 855 876, a plane of symmetry of the mid-axes of the magnet coils of the double magnet of the two electromagnetic control valves is arranged centrically with respect to a mid-axis of the pressure medium connection (there, the pressure medium inlet). In this case, the mid-axes of the two magnet coils at the same time also define the positions of the valve seats of the electromagnetic control valves of the pressure control valve arrangement, because the mid-axes of the magnet coils are arranged coaxially with the valve seats and with the magnet armatures. Furthermore, the valve seats of the electromagnetic control valves are connected to the pressure medium connection or issue into this via pressure medium ducts. These pressure medium ducts may be made coaxially with the mid-axes of the magnet coils by cutting manufacture, such as drilling, in order for reasons of cost to avoid having to rechuck the housing in order to make obliquely running pressure medium ducts or housing bores. The pressure medium ducts consequently run parallel to one another in a vertical direction.
So that the pressure medium ducts emanating from the valve seats of the electromagnetic control valves can therefore be manufactured in a vertical direction in the housing by cutting and at the same time both of them can issue into the pressure medium connection, the inside diameter of the pressure medium connection has to be relatively large, especially since the magnet coils also cannot undershoot a certain diameter. However, because a correspondingly large diameter of the pressure medium connection is unfavorable in flow terms, in practice a reducing sleeve which reduces the effective flow diameter is inserted into the pressure medium connection.
However, this procedure entails additional costs for producing and mounting the reducing sleeve, and, in view of the large number of pressure control valve arrangements delivered by a supplier of vehicles, this amounts in total to a relatively high sum.